1. Field of the Invention
The present invention relates to an integrated circuit package.
2. Description of Related Art
Integrated circuits are typically housed within a package which has a plurality of external contacts that are soldered to a printed circuit board. The package may also have a number of internal bond pads that are connected to corresponding pads of the integrated circuit by bond wires or a tape automated bonding (TAB) tape. The internal bond pads may be connected to the external contacts by routing layers and busses within the package. The busses and routing layers have conductive planes and traces that are dedicated to the power/ground busses and digital signal lines of the integrated circuit, respectively. By way of example, a conventional package may have a first bus layer dedicated to power, one or more routing layers dedicated to digital signals and a second bus layer dedicated to ground.
The various conductive layers are spatially located within different planes in the package. The layers are typically interconnected by conductive vias formed within the package. The bond pads may also be connected to the internal conductive layers by vias. Vias are typically formed by creating a hole in the dielectric package material and then plating the hole with a conductive material such as copper. The plating process is a relatively time consuming and expensive step. For this reason it is desirable to create an integrated circuit package with a minimal number of vias.
Some integrated circuits require power at different voltage levels. For example, an integrated circuit may require both 3.3 V and 2.0 V power. The additional voltage level requires an additional conductive power plane within the package. The second power plane can be created by forming an additional conductive layer within the package. The additional conductive layer requires more vias to connect the second power plane to the bond pads. It would be desirable to provide a dual voltage integrated circuit package which minimized the number of vias required to interconnect the pads and conductive layers of the package.
U.S. Pat. No. 5,557,502, issued to Banerjee et al., discloses an integrated circuit package which has a conductive strip that wraps around an edge of a bond shelf to interconnect a power bus to one or more bond pads on the shelf. The conductive strip is typically formed by initially masking all surfaces of the integrated circuit package except for the edge, and then dipping the package into a plating bath of copper. The plating bath plates copper onto the edge on the bond shelf.
The conductive copper strip extends continuously along the entire edge of the bond shelf. Because of this only one voltage level can be supplied to the contact pads located on the bond shelf with the plated edge. To provide more design flexibility it would be desirable to connect multiple power/ground planes to the bond pads on the bond shelf with the conductive strip.